Re: [PATCH 1/2] sha1_file: drop experimental GIT_USE_LOOKUP search
On Wed, Aug 09, 2017 at 11:12:19AM -0700, Junio C Hamano wrote: > Thanks for reducing the count of binary search functions by one. > > I think the "just one round of newton-raphson" in sha1_pos() comes > from [*1*]; I agree that it needs benchmarking before tweaking it. Actually, it's weirder than that. You mentioned it in that thread, but the code dates back much further. It was moved to the file in 96beef8, but that was just a copy from patch-ids.c. The original seems to be from 5d23e133d2 (Refactor patch-id filtering out of git-cherry and git-format-patch., 2007-04-09), which predates the sha1_entry_pos() experiment. I always thought those two sha1-lookup functions came in the opposite order, but I guess was wrong. Or possibly you are a time traveler. > We may want to tell libgit2 folks about this change, though [*2*]. > I think they too are carrying dead code that is only used under CPP > macro GIT_USE_LOOKUP, which they do not seem to define. Good thinking. It looks like they could use all three of the patches under discussion. I opened some PRs: https://github.com/libgit2/libgit2/pull/4326 https://github.com/libgit2/libgit2/pull/4327 https://github.com/libgit2/libgit2/pull/4328 -Peff
Re: [PATCH 1/2] sha1_file: drop experimental GIT_USE_LOOKUP search
Jeff King writes: > This lets us remove sha1_entry_pos() entirely, as the .idx > lookup code was the only caller. Note that sha1-lookup.c > still contains sha1_pos(), which differs from > sha1_entry_pos() in two ways: > > - it has a different interface; it uses a function pointer > to access sha1 entries rather than a size/offset pair > describing the table's memory layout > > - it only scales the initial selection of "mi", rather > than each iteration of the search > > We can't get rid of this function, as it's called from > several places. It may be that we could replace it with a > simple binary search, but that's out of scope for this patch > (and would need benchmarking). Thanks for reducing the count of binary search functions by one. I think the "just one round of newton-raphson" in sha1_pos() comes from [*1*]; I agree that it needs benchmarking before tweaking it. We may want to tell libgit2 folks about this change, though [*2*]. I think they too are carrying dead code that is only used under CPP macro GIT_USE_LOOKUP, which they do not seem to define. [Reference] *1* https://public-inbox.org/git/7v38vso8kz@alter.siamese.dyndns.org/ *2* https://github.com/libgit2/libgit2/commit/dd453c4dbf9a1fa38530b1f51e079852736b8f66
